Embodiments of the present invention generally relate to, and more particularly to implantable medical devices and more particularly to limiting over torque during active fixation.
Numerous medical devices exist today, including but not limited to electrocardiographs (“ECGs”), electroencephalographs (“EEGs”), squid magnetometers, implantable pacemakers, implantable cardioverter-defibrillators (“ICDs”), neurostimulators, electrophysiology (“EP”) mapping and radio frequency (“RF”) ablation systems, and the like. Implantable medical devices (hereafter generally “implantable medical devices” or “IMDs”) are configured to be implanted within patient anatomy and commonly employ one or more leads with electrodes that either receive or deliver voltage, current or other electromagnetic pulses (generally “energy”) from or to an organ or tissue for diagnostic or therapeutic purposes.
More recently, leadless IMDs (“LIMDs”) have been developed that are configured to be entirely implanted within a chamber of the heart through a nonsurgical procedure. Typically, an LIMD is introduced into the heart through a catheter. The LIMD includes a nonelectrical active fixation helix at the distal end, with the helix configured to be screwed into the heart wall in an area proximate to where it is desirable to deliver therapy. To implant the LIMD, a docking feature at the proximal end of the LIMD is temporarily connected to a docking cup at a distal end of the implant delivery catheter system. Once the LIMD is inserted into the heart chamber, the helix is secured to a desired point on the heart wall.
The physician seeks to ensure that the fixation helix is located against tissue of interest along the heart wall at an intended location. Once the physician confirms that the LIMD is located at an intended location, the physician rotates a knob on the implant delivery catheter (e.g. clockwise) at a number of turns to fixate/screw the fixation helix into the heart wall. Once the helix is properly fixated into tissue of the heart wall, the LIMD is released from the docking system and the implant delivery catheter system is removed from the patient.
When attaching the helix to tissue, a physician observes the LIMD through a series of fluoroscopy images while rotating the implant tool knob a predetermined or recommended number of turns. However, the process of attaching the helix by rotating the LIMD, while viewing a series of fluoroscopy images, presents a difficult or challenging procedure. As one example, it is difficult for the physician to know when the helix is embedded by a desired amount into the heart wall tissue, namely it is difficult to determine when the LIMD has been rotated enough. When too little rotation is applied, the LIMD may not be sufficiently fixated and dislodge at a later date. Alternatively, when excess rotation or over torqueing is applied, the helix may perforate the heart wall, particularly in regions where the heart wall is thin.